Hydroformylation reactions involve the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (synthesis gas) with carbon compounds containing olefinic unsaturation. The reaction is typically performed in the presence of a carbonylation catalyst and results in the formation of compounds, for example, aldehydes, which have one or more carbon atoms in their molecular structure than the starting olefinic feedstock. By way of example, higher alcohols may be produced in the so-called "oxo" process by hydroformylation of commercial C.sub.5 to C.sub.12 olefin fractions to an aldehyde-containing oxonation product, which on hydrogenation yields the corresponding C.sub.6 to C.sub.13 saturated alcohols. The oxo process is the commercial application of the hydroformylation reaction for making higher aldehydes and alcohols from olefins. The crude product of the hydroformylation reaction will typically contain catalyst, aldehydes, alcohols, unreacted olefin feed, synthesis gas and by-products.
The oxo process is well known in the art and is generally described in detail in Kirk-Other, Encyclopedia of Chemical Technology, Volume 16, 3rd edition, John Wiley & Sons, pp. 637-53, 1981. The teachings of U.S. Pat. No. 5,237,105 to Summerlin in regard to the oxo process are also incorporated herein by reference.
Prior to the hydrogenation step, the crude product of the oxo process is generally treated to remove the dissolved cobalt catalyst, which for reasons of economy may be recycled to the oxo reactor.
"Demetalled" hydroformylation reaction product or crude oxo aldehyde product is the reaction product which is substantially depleted of the transition metal cobalt catalyst required for the hydroformylation reaction. Such crude oxo aldehyde product will generally contain cobalt in an amount of from about 0.05 to 3.0 wt. %, calculated as elemental cobalt. The concentration of aldehyde in the crude oxo aldehyde product is generally from about 40 to 90 wt. %.
The next step in the oxo process is the hydrogenation of the crude oxo aldehyde product which is typically carried out in the presence of hydrogen and at pressures of about 6.89 MPa to 31.00 MPa (1000 to 4500 psig) using a hydrogenation catalyst.
The crude product of the oxo process is recovered then and, optionally, treated by known means to hydrogenate the aldehydes to form additional quantities of the corresponding oxo alcohols. These oxo alcohols, in turn, are widely used as chemical intermediates in the manufacture of plasticizers, detergents, solvents and the like.
The present inventors have developed a unique process which is capable of producing a higher yield of alcohols, as well as minimizing the amount of acid byproducts and dimer materials produced during the hydrogenation of oxo aldehydes. The present inventors have discovered that when hydrogenation is performed on a sulfided molybdenum-based catalyst such as NiMo, CoMo, NiCoMo, Mo and mixtures thereof, a higher yield and quality of alcohols can be obtained by recycling the output of one or more of the serially connected hydrogenation tank reactors back to the crude oxo aldehyde feedstream or, optionally, into a hydrogenation tank reactor connected in series with and preceding the hydrogenation tank reactor from which the recycle stream is taken.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings.